There has been, in the field of commercial carburetors, a struggle for smaller and smaller designs and lower and lower cost. When used in conjunction with internal combustion engines to power chain saws, small generators, and the like, the manufacturers have been competing with each other to reduce the size and weight of the overall structures. Thus, there has been pressure on the manufacturers of carburetors to decrease size, weight, and cost of the carburetors furnished.
The present invention is a product of this need to provide a small, inexpensive, lightweight carburetor. It is an object, therefore, to disclose a carburetor having a plastic body and which requires no fuel pump. The carburetor can be designated a self-lift carburetor which will draw fuel directly from a fuel tank without the aid of a pump and which will operate in any position relative to the fuel tank. This is sometimes referred to as an "all-position" carburetor.
Basic self-lift carburetors have been used in the early stages of power mowers, but the present design is for use with an all-position carburetor and the sophisticated design is believed to be the first self-lift unit to be adapted to this use.
Basically, the invention requires the use of a greatly increased diaphragm control valve spring rate and a venturi to create enough vacuum (signal) to overcome the spring to cause the fuel to flow into the carburetor, thereby eliminating the need for a fuel pump. In addition, an on-off check valve is interposed in the outlet of a diaphragm chamber to eliminate backflow of air into the metering chamber.
A further object of the invention relates to the use of a molded plastic carburetor body which eliminates machining and which incorporates some inserts to provide the necessary jets, fuel chambers and passages for full or partial throttle operation and for idling.
Other objects and features of the invention will be apparent in the following disclosure in which the invention is described in connection with details to enable a person skilled in the art to make and use the invention, all in connection with the best mode presently contemplated for the practice of the invention.